When using the new Tetranomicon v1.5.2 on a Minecraft 1.16.5 dedicated server, it crashes shortly after starting.
The error shown in the latest.log is the following:

net.minecraftforge.fml.LoadingFailedException: Loading errors encountered: [
	Tetranomicon (tetranomicon) has failed to load correctly
?7java.lang.NoClassDefFoundError: net/minecraft/client/util/ITooltipFlag
]

Tetranomicon v1.4 works without problems.

Attachment:
latest.log

PS:
Sorry to bother again. Client works fine btw, thank you : )

...and that's what I get for rushing a fix. on it!

Alright, hopefully 1.5.3 should fix this, but the dev environment is being irritatingly obtuse about testing it. I've posted it to CurseForge. Give it a try when it goes public and let me know if it works for people other than me.

v1.5.3 works like a charm on my dedicated server (or at least it loads and I can connect), so what you did seems to have worked.
Thanks again for fixing this so fast and have a nice day/night : )